The present invention relates to a method and to a cellular telecommunication apparatus for displaying the local time.
Cellular phones are frequently used today, and one common feature is the internal watch/clock which enables the user to monitor the present time. The watch/clock is hereafter referred to as clock. The internal clock is often very accurate, which makes this feature very useful. However, when travelling between different time zones, the clock must be changed every time the phone is entering another time zone, in order to display the correct time in the present time zone. This means that the user must set a new time in the clock, if he/she would like to monitor the actual time. If the user is travelling between different time zones, it might become very annoying if you forget to set the clock in accordance with the actual time difference. Therefore, it is desirable for a phone, which is able to display the time, to be automatically adjusted to the standard time where its used.
U.S. Pat. No. 5,375,104 discloses a mobile terminal equipment, which is able to display the local time within geographical areas having different time zones. The equipment uses an IC-card to store time differences between a standard time zone and a main area. When the user enters a new time zone, the equipment receives locational information, which is stored in a ROM memory. Thereafter, the equipment should be able to locate the standard time zone on the IC-card, calculate the time difference, and display the result on the equipment. However, this means that when using the IC-card, it is required to establish some kind of database on the IC-card, and have a routine to handle the data when calculating the actual time for each geographical area having a different time zone than the main area. Also, the time differences are stored on the IC-card, which take up valuable space in the memory. For example, an IC-card in a GSM telephone could be equal to the SIM (subscriber identity module) card, which is used in this type of telephones, and has a very restricted amount of memory. Thus, it is desirable to avoid using, or at least save valuable memory space on such cards. Also, it is desirable to simplify the calculation of the local time.
WO 90/13983 discloses a portable receiver, e.g. a pager, which has a time of day clock. The portable receiver receives a signal indicative of the location of the receiver, which determines the time zone of the location and the time zone of the time of day clock. The time of day clock is adjusted to correspond to the time zone of location. However, as described in U.S. Pat. No. 5,375,104, this requires that the pager has a memory provided with information of different time zones, which is a disadvantage when handling the received data.
EP-B1-0,475,298 discloses a further example of adjusting a clock in a cellular phone, by means of a memory provided with information of different time zones.
GB-A-2,284,965 mentions that it is possible to receive time data from a base station, which allows the telephone to recalibrate its own time in accordance with the reference time data of that base station.
The main object of the present invention is to provide a phone, which is able to display the time, to be automatically adjusted to the standard time of its use. Another object is to avoid using valuable memory space in the phone or a card to be inserted in the phone. Also, it is an object to simplify the calculation of the local time.
These objects are achieved in accordance with the present invention by claims 1, and 6, respectively.
One particular advantage of the invention is that the clock in the phone does not have to be recalibrated, since the only change which will occur on the display is the indication of hours. The clock in the phone is mostly very accurate. This means that, if the clock is recalibrated, the time indicated on the display may differ from original clock settings. Thus, this is a very good feature, when the user is comfortable with the clock settings, and is only interested to change the hours of the indicated time, the user does not have to be worried about any changes of the time which is beyond the user""s knowledge.
Further advantages of the present invention will be apparent from the dependent claims.